Chemistry Reference
In-Depth Information
derivatives results in the formation of supramolecular polymers featuring liquid
crystalline ordering (Fig. 1.1). Lehn and coworkers later extended this strategy
to include bifunctional molecules joined by chiral tartaric acid spacers
(Gulikkrzywicki et al. 1993) and rigid anthracene-based linkers (Kotera et al.
1995). This approach is quite general, as can be seen in later chapters of this topic.
The work done by E. W. Meijer using self-complementary ureidopyrimidinones
builds upon Lehn's supramolecular polymers (Sijbesma et al. 1997). The quadruple
hydrogen bonding system employed in these studies has two major differences from
Lehn's polymers: 1) a high degree of association (K
dim
. 10
6
M
21
) and 2) self-
complementarity that eliminates stoichiometric concerns. The high dimerization con-
stant of ureidopyrimidinones makes this recognition element an excellent choice
for supramolecular polymerizations, providing a high degree of polymerization
in solution.
An alternative approach to supramolecular polymers is provided by covalently
attaching recognition elements to the polymer backbone. These polymers can then
be used as macromonomers for higher level polymer assembly or for “plug and
Figure 1.1 (a) Supramolecular polymers developed by Lehn using three-point hydrogen
bonds between diamidopyridine and thymine residues and (b) analogous polymers by
Meijer employing self-complementary, quadruple hydrogen bonds. (c) A schematic depiction
of the extended chain of repeating bisfunctional monomers forming the backbone of supra-
molecular polymers.
